Telephone system



June 10, 1941; H. DOHLE 2,244,906

TELEPHONE SYSTEM I Filed Jan. '3, 1938 a 55 INVENTOR.

' ATTORNEY.

Patented June 10, 1941 UNITED STATES PATENT GFFICE TELEPHONE SYSTEM Hinrich Diihle, Altglienicke, near Berlin, Germany, assignor to ,Teleph'on-Apparat Fabrik E. Zwietusch and '00. G. m. b. H., Charlottenburg, Berlin, Germany Application January 3, 1938, Serial No. 182,987 In Germany January 25, 1937 8 Claims.

The subject of the invention is a circuit arrangement for limiting the duration of calls at telephone stations in which an extension of the time allowed for calling can be obtained by a switching measure on the part of the user which influences the automatic charging device. Circuit arrangements are known in which the time switch determining the duration of a call is arranged at the individual stations. The invention relates to a circuit arrangement in which the duration vof the call is determined by a time switch in the exchange and relates in particular to the switching devices governing the control of this time switch. The invention enables the time switch to be controlled from the telephone station over the speaking leads without interfering with the balance of the speaking leads during the .existence of the call.

According to the invention this is achieved in that the blocking efiect of the time switch which limits the duration of the call is neutralized by a relay connected in the line leading to the exchange and possessing two dilierential windings which is caused to operate through the deenergization of one winding when an additional fee is paid and locks up over its own contact independently of the time switch.

An embodiment of the invention is represented in the single sheet of circuit drawings, which disclose a paystation operating on the press button principle whose line extends to an automatic telephone exchange of the usual type. Of the exchange devices only those serving to limit the duration of calls are indicated.

In the drawings the reference characters have the .following significance: The switchhook contacts are represented by IHU and 2HU, these being under the influence of a delay device in order in the known way to prevent dialling by means of the switchhook. nsz indicates the dial impulse contact and nsa. the dial off-normal contact. die is an off-normal contact which is switched over as soon as the dial is drawn round and remains operated until the receiver is replaced. MF represents a coin-testing lever operated by the time switch. It closes if no coin has been inserted in the apparatus when the dial plate is operated. mic is a. coin contact which is transitorily closed when the coin which has been inserted in the apparatus, and which lies in an intermediate posltion, is advanced into the collecting chamber on the depression of the connecting key KT.

The switching devices in the exchange serving to limit the duration of the call consist of the relays D and X and a stepping switch ZS. The

stepping switch ZS possesses 35 contacts and is driven by a magnet MZS. The mode of operation of the circuit is as follows:

On the removal of the receiver a loop is closed to'the exchange. In the case of an outgoing call the contact die is switched over when the dial is operated so as to interrupt the feeding current for the microphone Mi by the condenser C. The exchange loop is maintained over the bell W. The current flowing over the exchange loop and the control relays GA and GB in the group selector GW energizes relay X. Relay D, however, does not energize because the windings DI and 1311 are connected in opposition. As soon as the called subscriber replies the calling party must depress the connecting key KT so as to enable the microphone Mi to receive feeding current. The key KT remains in the operated position until the receiver is replaced. Through the depression of the key KT the coin which occupies an intermediate position is advanced into the collecting chamber and consequently the contact mic is temporarily closed. By means of contact mic winding D11 is deenergized so that the relay operates over winding DI. After contact mic has opened the relay D remains up for the time being because winding D11 is short-circuited by contact 4d. Relay A is connected over contact 3d to the interrupter U which operates at 5 seconds intervals. The rotary magnet MZ'S is energized over contact a so that each time relay A pulls up the wiper ZS is moved to the next contact. As soon as the wiper has passed from position 0 to position 1, relay D releases because its winding DI is short-circuited over ZS in position 1 and contact id. After relay D has released relay A remains connected to the interrupter U over Iss0 and lzs35. The contacts zsll and zs35 are so-called rotary ofi-normal contacts of the switch ZS, and of these Izsfl and Zzsll are closed in position 0, while in position 35 contact lzs35 opens and contact 22835 closes. On step 32 shortly before the expiry of the prescribed call period a warning signal SU is transmitted to the subscriber over condenser Cl. In the following interval during which the time switch passes to step 35 the calling party must pay in an additional fee if he wishes to prolong the conversation. For this purpose another coin is inserted so that relay D energizes because winding DH is short-circuited by earth over contact mic. Winding DH is short-circuited over contact 4d until the switch ZS has reached contact 0. On the expiry of the prescribed eriod the rotary offnormal contact lzs35 is opened and the energizing circuit for relay A is broken so that the stepping switch ZS remains on contact 35 until relay D operates in response to the subscriber inserting another coin to extend the conversation period or until relay X releases through the replacement of the receiver. At contact 22835 the speaking leads are bridged .by the high capacity condenser C3 and conversation is rendered impossible by the application of a buzzer Su to the speaking leads over contact 35.

In this way, on the expiry of the prescribed period the existing connection is not interrupted but only the intelligibility destroyed, so that even after the normal period has expired this may be extended by a further payment. When relay 1X releases through the replacement of the receiver, relay A operates with the rotary magnet MZSa an automatic interrupter until the circuit-passing over mes, Ix, Iss0 and A is broken a t Iss0 when the switch ZS reaches the zero position."

What is claimed is: l

1. In a telephone system, an exchange, a calling line and a called line terminating at said exchange, means in'said exchange for completing a connection between said lines, a device required to be operated by one of the subscribers before beginning conversation over said connection, means controlled by said device for timing said conversation, a condenser in said exchange, and means controlled by said timing means for bridging the connection with said condenser after an interval of time thereby to interrupt conversation thereover.

2. In a telephone system, a calling line and a called line, means for completing a connection therebetween, a device required to be operated by one of the subscribers before beginning conversation over said connection, means controlled by said device for timing said conversation, and means controlled by said timing means for impressing an audible tone upon the connection after an interval of time thereby to render conversation thereover difficult, said device reoperable by said one subscriber to control said timing means to cause said tone to be removed from said connection.

3. In a telephone system, a calling line and a called line, means for completing a connection therebetween, a condenser, a source of audible tone, a device required to be operated by one of the subscribers before beginning conversation over the connection, and means controlled by said device for timing said conversation, said timing means effective after a predetermined interval both to cause the connection to be bridged with said condenser and, concurrently with the bridging of said connection with the condenser, to impress tone from said source upon the connection thereby to interrupt conversation thereover.

4. In a telephone system, a calling line and a called line, means for completing a connection therebetween, a device required to be transitorily operated by one of the subscribers before beginning conversation, a two-winding relay included serially in said connection and controlled over one of said lines by said device to initiate the timing of said conversation, and means for interrupting said conversation after an interval of time, said device then reoperable to control said relay both to cause said last means to be rendered inefiective and to initiate the timing of an extension of said conversation.

5.,A telephone system as claimed in claim 4 wherein the means for interrupting said connection with said condenser.

'6. A telephone system as claimed in claim 4 wherein the means for interrupting said conversation after said interval of time comprises an audible tone and means controlled by said timing means for impressing said tone upon the connection to render conversation thereover difiicult. g

7. In a telephone system a calling line and a called line, means for completing a connection ther'ebetween a differential relay having one winding in series with each conductor of the connection, timing means, a device required to be operated transitorily by one of the subscribers before beginning conversation over the connection thereby to initially operate'said relay, said relay effective upon operation to initiate the operation of said timing means and to lock itself in operated position under control of said timing means, said timing means effective firstto release said relay and then after an interval of time to interrupt said conversation if said relay.

is not reoperated by said one subscriber under control of said device.

8. In a telephone system, a calling line and 9. called line, means for completing a connection therebetween to permit the two subscribers to converse, a condenser, timing means, means controlled by said timing means for causing said condenser to be bridged across said connection after an interval of time tointerrupt the conversation, a difierential relay having one winding in series with each conductor of the connection, a device transitorily operable by one of the subscribers and eiTective to initially operate'said relay, said relay effective both to initiate an additional timing operation of said timing means thereby to cause the condenser bridge across said connection to be removed and also to'lockit'self operated under the control of said timing means.

HINRICH DoHL i 

